Combination Sum

Leetcode 39.

In order to achieve the unique combinations of candidates, for loop should start with the specified value named start. This operation is usually called Pruning

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class Solution {
    public List<List<Integer>> combinationSum(int[] candidates, int target) {
       
       List<List<Integer>> ans = new ArrayList<>();
       List<Integer> list = new ArrayList<>();
       backtricking(candidates,target,list,ans,0);
       return ans;
    }
    public void backtricking(int[] candidates,int target, List<Integer> list,List<List<Integer>> ans,int start){
       //recursion stop condition 
       if(target <= 0){
           if(target == 0)
             ans.add(new ArrayList<>(list));
          return;
       }
       
       //for loop for this layer 
       //for loop start with the specified value named start
       //Pruning
       for(int i = start; i < candidates.length;i++){
          //process the nodes 
          list.add(candidates[i]);
          target -= candidates[i];
          //recursion 
          backtricking(candidates,target,list,ans,i);
          //undo the previous operations 
          list.remove(list.size() - 1);
          target += candidates[i];       
       }

    }
}